Research on hub motor control of four-wheel drive electric vehicle

The Four-wheel drive electric vehicle (EV) is driven by four hub motors. In the hub motor drive system, three hall-effect sensors are usually used to provide absolute rotor position information, correspond to the block commutation algorithm for BLDC motors. However, the waveform of the back electromotive force (EMF) of the hub motor is not trapezoidal, but between sinusoidal and trapezoidal shape. The amplitude of the torque ripple at low speed is large and the frequency is close to resonant frequency. As a result, when the EV drives at low speed, the noise is serious. A sinusoidal current drive system of sinusoidal-wave PM motor with a low resolution position sensor is proposed in paper [1]. At low speed, the performance of the sinusoidal current control is perfect, and the torque ripple is much lower than that of the block commutation algorithm. However, the noise increases at middle and high speed because of the switching noise and harmonics. This paper proposes a combined BLDC and PMSM control for the hub motors. Sinusoidal control or field oriented control is applied for the hub motor at low speed, while block commutation algorithm is used at middle and high speed. A low noise level of the driving cab in all speed range can be reached. The electric braking method for the Four-wheel drive EV is also introduced. The proposed methodology is demonstrated by vehicle test, and is shown to achieve low noise level and dynamic performance.